Electronic parts such as hybrid packages, multimodules, and integrated circuits sealed with a plastic or metal have come to generate a larger amount of heat as a result of the progress in the degree of integration in IC's, etc. Due to the enhanced increase in temperature, there is a fear that such electronic parts may have a functional fault. A generally employed technique for avoiding this trouble is to attach a radiating member, e.g., a heat sink, to an electronic part by means of an appropriate adhesive material.
Many adhesive materials for use in the above application are known. Examples thereof include an adhesive comprising an acrylic monomer, aluminum particles, and a polymerization initiator (see U.S. Pat. No. 4,722,960), an electroconductive adhesive tape in which the adhesive layer contains silver particles having a diameter larger than the thickness of the adhesive layer (see U.S. Pat. No. 4,606,962), and a heat-conductive, electrical insulating, pressure-sensitive adhesive comprising an acrylic polymer having polar groups and a heat-conductive filler randomly dispersed in the polymer (see JP-A-6-88061 which corresponds to EP 566093 A1). The term "JP-A" as used herein means an "unexamined published Japanese patent application".
Recently, radiating members, e.g., heat sinks, which have been bonded with an adhesive to electronic parts are frequently detached therefrom for reuse when the electronic parts are discarded or subjected to module exchange. In this case, the adhesive material is required not only to have tight adhesion during use to satisfactorily perform its fixing function, but to have easy peeling which enables the radiating members to be easily detached when the electronic parts are discarded or subjected to module exchange. However, none of the known adhesive materials described above can meet these requirements.
Known design ideas which have been employed for controlling adhesive properties are to reduce adhesive strength by increasing crosslinking density and to improve wetting ability by softening. However, the former technique, based on increasing crosslinking density, reduces wetting ability to impair adhesion to adherends, while the latter technique, based on softening, causes an increase in adhesive strength. Consequently, it is exceedingly difficult to use the design ideas described above for obtaining tight adhesion during use and obtaining easy peeling at the time of discarding or module exchange as described above, i.e., for obtaining both of the two properties.
Under these circumstances, a curable pressure-sensitive adhesive has been proposed in JP-A-56-61468, JP-B-1-53989, JP-B-2-42393, etc. The term "JP-B" as used herein means an "examined Japanese patent publication". This curable adhesive has been designed to be in a soft state for attaining high adhesive strength in the initial stage and to be capable of being reduced in adhesive strength at the time of detachment by increasing the crosslinking density of the adhesive through curing treatment with light or heat or by foaming the adhesive. However, such pressure-sensitive adhesives have drawbacks, for example, that they necessitate the step of treatment with light or heat to complicate the process, equipment, etc., and that the applications thereof are limited because of limited allowable conditions therefor.